kafka中Preferred Leader设置

https://www.pianshen.com/article/12231023160/

broker重启后可能会有异常，比如Preferred Leader由true变为flase

在创建一个topic时，kafka尽量将partition均分在所有的brokers上，并且将replicas也j均分在不同的broker上。

每个partitiion的所有replicas叫做"assigned replicas"，"assigned replicas"中的第一个replicas叫"preferred replica"，刚创建的topic一般"preferred replica"是leader。leader replica负责所有的读写。

但随着时间推移，broker可能会停机，会导致leader迁移，导致机群的负载不均衡。我们期望对topic的leader进行重新负载均衡，让partition选择"preferred replica"做为leader。

用kafka-eagle监控kafka运行状况，分区3所在的broker异常重启了。截图看看，分区3的Preferred Leader为false，由于Replicas为[1,3,4]，leader为3，由于leader为副本3，副本3不是Replicas里的第一个副本（副本1），所以Preferred Leader为false。

有两种方法可以让Preferred Leader恢复为true

方法一：修改leader为副本1
方法二：调整Replicas的副本集顺序为[3,1,4]

我们用方法二试试

#cat move.json
{
"partitions": [
{
"topic": "data_report_h5_merged_app",
"partition": 3,
"replicas": [
3,
1,
4
]
}]
}

#

/usr/local/xyhadoop/kafka/bin/kafka-reassign-partitions.sh --zookeeper localhost:2181/kafka --reassignment-json-file move.json --execute
Current partition replica assignment

{"version":1,"partitions":[{"topic":"data_report_h5_merged_app","partition":2,"replicas":[1,2,3],"log_dirs":["any","any","any"]},{"topic":"data_report_h5_merged_app","partition":4,"replicas":[3,4,5],"log_dirs":["any","any","any"]},{"topic":"data_report_h5_merged_app","partition":1,"replicas":[5,1,2],"log_dirs":["any","any","any"]},{"topic":"data_report_h5_merged_app","partition":5,"replicas":[4,1,2],"log_dirs":["any","any","any"]},{"topic":"data_report_h5_merged_app","partition":7,"replicas":[1,3,4],"log_dirs":["any","any","any"]},{"topic":"data_report_h5_merged_app","partition":0,"replicas":[4,5,1],"log_dirs":["any","any","any"]},{"topic":"data_report_h5_merged_app","partition":3,"replicas":[1,3,4],"log_dirs":["any","any","any"]},{"topic":"data_report_h5_merged_app","partition":6,"replicas":[5,2,3],"log_dirs":["any","any","any"]}]}

Save this to use as the --reassignment-json-file option during rollback
Successfully started reassignment of partitions.

再看看kafka-eagle，已经 Preferred Leader恢复为true

案例2：

对所有Topics进行操作

./bin/kafka-preferred-replica-election.sh --zookeeper hadoop16:2181,hadoop17:2181,hadoop18:2181/kafka08

对某个Topic进行操作

[sankuai@data-kafka01 kafka]$ cat topicPartitionList.json

{

"partitions":

[

{"topic":"test.example","partition": "0"}

]

}

./bin/kafka-preferred-replica-election.sh --zookeeper hadoop16:2181,hadoop17:2181,hadoop18:2181/kafka08 --path-to-json-file topicPartitionList.json